The present invention relates generally to methods for growing high quality crystals of gallium arsenide for use in the fabrication of electronic and opto-electronic devices. More particularly, the present invention relates to methods for growing gallium arsenide crystals by forming thin films of gallium arsenide on a substrate.
There has been an increasing demand for gallium arsenide crystals which are suitable for use in fabricating electronic and opto-electronic devices, as well as solar cells. Accordingly, there has been a great deal of interest in developing simple, effective and reliable techniques for producing high quality gallium arsenide crystals.
Most of the methods presently being used to grow gallium arsenide crystals are either based upon bulk crystal growth or epitaxial techniques. The bulk crystal growth processes are generally based upon the Czochralski or Bridgman methods. Both of these methods basically involve heating a mixture of gallium and arsenic to form a melt of gallium arsenide. A seed crystal is then dipped into the melt. The seed is allowed to melt back a short distance to remove any surface imperfections which may result from its preparation. The seed crystal is then slowly withdrawn from the melt. The rate of seed crystal withdrawal and melt temperature are closely controlled so that a single pure crystal of gallium arsenide is pulled from the melt. This type of bulk crystal growing technique has widely been used for growing various other crystals and the numerous inherent advantages and disadvantages of this technique are well documented.
Both liquid phase and gas phase epitaxy have been used in the past to deposit thin films of pure gallium arsenide on bulk gallium arsenide wafers or substrates. In general, these epitaxial techniques have involved either chemical or thermal treatment of gallium arsenide and gallium arsenide precursors present in the gas or liquid phase to form gallium arsenide which is deposited as a thin ultra-pure crystal on the gallium arsenide substrate. In addition, molecular beam epitaxy has been utilized in growing gallium arsenide crystals. Molecular beam epitaxy basically involves heating gallium metal and arsenic metal to high temperatures in order to form gallium and arsenide atoms. The metal atoms are transmitted to the surface of a bulk gallium arsenide wafer to form thin films of ultra-pure gallium arsenide.
The presently available methods for growing gallium arsenide crystals are well suited for their intended purpose; however, none of the presently available methods have been entirely successful commercially. This lack of commercial success is due in part to various different problems which are inherent in the presently available methods. Accordingly, there is a continuing need to provide methods which are capable of producing commercial quantities of high quality gallium arsenide crystals which are suitable for use in the fabrication of semiconductor devices.